Multi-spot-beam satellite system with broadcast and surge capacity capability

ABSTRACT

A payload design for a multi-spot-beam satellite communication system includes a plurality of uplink spot beam receivers and downlink spot beam transmitters, and a broadcast transmitting subsystem capable of transmitting a broadcast beam to an entire system geographical service area. An input filter-switch-matrix (IFSM) controllably selects input IF signal bands for routing to an on-board digital signal processor-router (DSPR). The DSPR subsequently routes all received point-to-point and broadcast data packets to the appropriate downlink spot or broadcast transmitting subsystems for transmission thereof. The broadcast downlink allows broadcast transmissions to occur at the highest efficiency possible, while also allowing for flexible provision of surge capacity for point-to-point transmissions on previously exhausted spot beams by selective use of the broadcast beam for such point-to-point transmissions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 09/605,775, filed Jun. 28,2000 now U.S. Pat No. 6,704,544 which was a continuation of applicationSer. No. 08/882,119 filed Jun. 25, 1997, now issued as U.S. Pat. No.6,175,719 on Jan. 16, 2001, the entire contents of both applicationsbeing incorporated herein by this reference.

TECHNICAL FIELD

The present invention relates to multi-spot-beam satellite communicationsystems, and more particularly to a satellite payload arranged toprovide broadcast and surge-capacity capability to multi-spot-beamsatellite communication systems.

BACKGROUND ART

Generally, an emerging use of wide-band communication systems employingextremely high frequency Ka or V frequency bands is leading todevelopment and implementation of commercial satellite systems whichsupport a large number of high-gain spot beams. Because of high reuse ofthe available frequency spectrum, spot beam technology advantageouslyallows high capacity systems to be realized with a finite number ofbeams. For example, the primary frequency spectrum of the orbit slot istypically divided up equally among several spot beams to form afrequency reuse cluster, e.g., four beams per cluster. Spot beamtechnology also permits reduction of ground terminal size to a pointwhere such terminals become commercially feasible as a mass-marketend-user terminal.

In known payload designs for multi-beam systems, total capacity of thesatellite is generally divided and allocated among the beams on apreferably equal basis so as to accommodate design simplification andcost reductions as well as changes in user demand and market needs. As aresult, such payloads achieve maximum total throughput only when used insupport of point-to-point (PTP) transmissions having an even trafficdistribution among the respective beams at their individual fullcapacities. However, such even distribution is inherently unrealisticbecause certain geographic areas naturally have a higher use demand thanothers. In addition, changing market conditions and other networkingfactors directly impact the distribution of a system's traffic load.Thus, known multi-beam systems operate with a significantly reducedeffective utilization of the satellite capacity when compared to thecapacity with which the beams could otherwise collectively support.

Another drawback to known multi-beam systems and payload designs whichare inherently suited for PTP transmissions is the loss of throughputefficiency when such systems are used to support broadcast transmissionsto be sent to the entire geographic service area. Typically, suchsystems can only provide broadcast capability if the desired broadcastinformation is individually transmitted on every spot beam in thesystem.

DISCLOSURE OF THE INVENTION

Therefore, it is an object of the present invention to provide amulti-spot-beam satellite communication system and method havingimproved utilization of system capacity.

Another object of the present invention to provide a payload design fora multi-spot-beam satellite communication system which can support bothpoint-to-point and broadcast transmissions at an optimum transmissionefficiency.

Still another object of the present invention to provide a payloaddesign for a multi-spot-beam satellite communication system which canflexibly utilize up to all of a system's broadcast capacity as a surgemechanism to support point-to-point traffic for either uplink ordownlink transmissions for any spot beam whose capacity has beenexhausted.

In accordance with these and other objects, a first aspect of thepresent invention provides a method of configuring a satellite payloadfor use in a multi-spot-beam communication system including the steps ofproviding a plurality of spot-beam uplinks each of which receive signalstransmitted from a particular section of a total geographic area to beserviced by the communication system, providing a plurality of spot-beamdownlinks each of which transmits signals to a particular section of thetotal service area, and providing a broadcast downlink which transmits asingle wide-area beam to the total service area. Point-to-point servicesare supported by routing point-to-point transmissions received by theplurality of uplinks to a particular one of the plurality of downlinks,while broadcast services are supported by routing broadcasttransmissions received by the plurality of uplinks to the broadcasttransmission link in a non-blocking manner. In addition, the methodfurther can include the step of providing a surge mechanism by routingto the broadcast downlink point-to-point transmissions of any of theplurality of spot-beam uplinks and spot-beam downlinks whosetransmission capacity is exhausted.

In accordance with another aspect of the present invention, a payloadfor use with a multi-spot-beam communication system includes a pluralityof receiving spot-beam antenna subsystems each arranged to receivesignals transmitted from a particular section of a total geographic areato be covered by the communication system, a receiver means connected tothe plurality of receiving spot-beam antenna subsystems for convertingeach received signal to an intermediate frequency, and a plurality oftransmitting spot-beam antenna subsystems each arranged to transmitsignals to a particular section of the total service area. An on-boardprocessor is connected to the receiver means and the plurality oftransmitting spot-beam antenna subsystems for selectively routingreceived signals to a particular transmitting spot-beam antennasubsystem. A broadcast transmitter subsystem is connected to theon-board processor and arranged to transmit signals to the total servicearea, while an input-filter-switch-matrix is connected to the receivermeans and the onboard processor for selectively routing bands ofreceived signals to the on-board processor in a non-blocking manner fortransmission by the broadcast transmitter subsystem.

The above objects and other objects, features, and advantages of thepresent invention are readily apparent from the following detaileddescription of the best mode for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the foot-print and layout of a multi-spot-beam satellitecommunication system in accordance with the present invention;

FIG. 2 shows a block diagram of a satellite payload in accordance withthe present invention; and

FIG. 3 shows a block diagram of a satellite payload in accordance with asecond embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, a multi-spot-beam satellite communication system 10is shown having a total service geographic area 12 covered by arelatively large number of uplink and downlink spot beams havingindividual foot-prints 14. High-gain uplink spot beams are preferablyutilized to support small low-power, low cost, end-user earth stationterminals 16, while high-gain downlink spot beams are utilized tosupport high-data-rate transmission to the same small end-user terminals16. More importantly, the combination of uplink and downlink spot beamsprovides for multiple reuse of the same limited frequency spectrum by asingle large satellite 18, thus creating a high-capacity system whichcan serve mass markets for numerous communications services. A networkcontrol center (NCC) 20 provides overall transmission control anduplink/downlink frequency assignment for end users 16 and satellite 18.

In accordance with the present invention, an area-wide broadcastdownlink beam 22 is integrated into a satellite payload system design100 as shown in FIG. 2. System 100 includes a plurality (i) ofconventional uplink receiver subsystems 102 and a corresponding numberof conventional downlink transmitter amplifier subsystems 104. Thenumber of subsystems 102 and 104 can be any number selected for thesystem based on its design, intended use, cost, and the like. Eachuplink receiver subsystem 102 includes a spot beam antenna 106, anorthogonal mode transducer (OMT) 108 (which separates signals ofopposite polarizations), and a combination of a low noise amplifier(LNA) 110, and a downconverter (D/C) 112. While only one combinationLNA/UC is shown for each uplink receive subsystem 102, a combinationLNA/UC is provided for each of the two signal polarizations received byantenna 102 and 108. For point-to-point (PTP) traffic, each downlinktransmit subsystem 104 includes an upconverter (U/C) 114, an amplifier116, and a spot beam antenna 118. The operation and design of subsystems102 and 104 is well understood in the art.

An on-board digital signal processor-router (DSPR) 120 preferablyprovides appropriate demodulation, routing/switching, multiplexing, andmodulation of traffic data packets received by satellite 18 intotime-division-multiplexed (TDM) signals. More specifically, all PTPtransmissions (which are sent in the form of data packets) originatingfrom a particular spot or footprint are received by a corresponding oneof the antennas 106 and receiver subsystems 102 and converted to anintermediate frequency (IF) signal. DSPR 120 then processes and groupsthe data packets into individual signals for delivery via an output portto a particular one of the transmitter amplifier subsystems 104 andantennas 118 for subsequent transmission to the designated or addressedspot area.

In addition to subsystems 104 and corresponding antennas 118, system 100includes a broadcast downlink antenna 122, an output-filter multiplexer(OMUX) 130, and a number of broadcast transmitter amplifier subsystems124 connected to a plurality of DSPR 120 output ports. Broadcast antenna122 transmits broadcast beam 22 so that all individual users in everyspot area within service area 12 can receive the broadcasttransmissions. Each broadcast transmitter amplifier subsystem 124includes a set of upconverters (U/C) 126 and amplifiers 128 similar toupconverters 114 and amplifiers 116. OMUX 130 supplies the plurality ofbroadcast signals to broadcast antenna 122.

In further accordance with the present invention, each receiversubsystem 102 is preferably designed to receive the entire primaryfrequency bandwidth of system 10. This contrasts with known spot-beamreceiver subsystems which typically only receive a fixed, individualsub-band. A reconfigurable input filter-switch-matrix (IFSM) 132 isconnected to the plurality of receiver subsystems 102 and the DSPR 120and is controllable via an NCC input 134 and a command decoder 136 toselect any predefined band of each IF frequency spectrum, and connectthe selected bands to appropriate output ports in a non-blockingfashion.

FIG. 3 discloses a second embodiment 200 of the present invention wherelike elements to those previously described are denoted with the samereference numbers. System 200 is arranged to accommodate existing DSPRand satellite designs while at the same time provide broadcasttransmission and surge handling capabilities, and improve systemutilization and efficiency.

More specifically, system 200 is arranged to operate with a systemfrequency plan which allocates the full primary system spectrum of onepolarization to uplink-downlink spot-beams for PTP transmissions, whilethe full primary spectrum of the opposite polarization is allocated forbroadcast transmissions utilized with the broadcast downlink beam. Inaddition, the broadcast spectrum is assignable in minimum-resolutionbroadcast (MRB) bands, which are assignable to any and all uplink spotbeams in any combination as configured by NCC 20.

Further, DSPR input/output ports are assumed to have a fixed amount ofbandwidth processing capability equal to 1/K of the primary systemspectrum on one polarization, where K is the number of MRBs fitting intothe primary spectrum. Spot beams on the broadcast polarization will bereceived at the satellite by a plurality of receiver subsystems 202having a bandwidth equal to the full primary spectrum. Morespecifically, each receiver subsystem 202 is connected to acorresponding OMT 108 in one of the receiver subsystems 102, and to aninput of IFSM 132. Each receiver subsystem 202 includes a set of LNAs204 and downconverters (D/C) 206 similar to LNAs 110 and D/Cs 112.

IFSM 132 is controlled by ground commands to select a fixed bandwidthequal to the DSPR input port capacity (i.e., 1/K of primary spectrum)that corresponds to each individual spot beam for PTP traffic, andconnects each to a pre-assigned output port for input to a dedicatedinput port of DSPR 120. At the same time, IFSM 132 can be configured byNCC 20 to select any number of MRB frequency bands from each IF signalof each full-band receiver subsystem 202, and deliver each selected MRBband to one of several output ports. As such, the input and output portsof IFSM 132 and DSPR 120 are generally different in their bandwidthhandling capability when used with PTP or broadcast receive/transmitsubsystems.

With the embodiment shown in FIG. 3, the output broadcast ports of DSPR120 as a set cannot support more bandwidth than the total spectrumallocated to the broadcast transmissions in the downlink. This meansthat the total number of MRB frequency bands selected from all of thereceived full-band IF signals from all spot beams at any instant cannotcarry more user data packets than can be correspondingly carried in theset of broadcast TDM streams. Further, every spot beam can access thesatellite broadcast section in increments of one MRB up to the fullprimary spectrum, if so configured by NCC 20, and can transmit on all ora portion of a MRB as needed. Thus, depending on the amount of surgecapacity required by each spot, in either the uplink or downlinkdirection, the satellite payload can be configured to deliver thenecessary additional capacity.

Therefore, the addition and integration of the broadcast downlink beamin accordance with the present invention overcomes the aforementionedshortcomings of conventional multi-spot-beam system designs. Morespecifically, the present invention provides a system which can supportall broadcast applications/services at a significantly highertransmission efficiency than otherwise possible through the spot beams.This is achieved because by carrying broadcast services over thebroadcast channels, more of the capacity of each spot beam is availablefor PTP traffic. In addition, the broadcast capacity, accessible to allsystem users in all spot beams, can be selectively used as a surgemechanism to provide additional uplink/downlink capacity to any spotbeam for PTP traffic when the PTP capacity of a particular beam is fullyexhausted. Thus, unpredictable changing market needs and trafficdistribution can be met by assigning capacity to the right mix ofservices and locations throughout the system life cycle. Finally, havingthe surge and broadcast capacity to assign to different beams alsooptimizes the effective utilization of the total satellite capacity. Inother words, use of the surge capacity to continue to keep in service anotherwise exhausted spot beam will inherently increase the utilizationof every other spot beam, and thus that of the whole system.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

1. A method for improving utilization of satellite capacity of asatellite system that uses multiple uplink spot beams and downlink spotbeams, comprising: switching from operating one or more of the multiplespot beams of a satellite whose transmission capacity has been exhaustedto operating area-wide broadcast downlink beam of the satellite forsupporting point-to-point transmissions of the one or more of themultiple spot beams of the satellite whose transmission capacity hasbeen exhausted.
 2. A method as recited in claim 1, further comprising:allocating a full primary spectrum of one polarization to uplink anddownlink spot beams for point-to-point transmissions, and allocating afull primary spectrum of a polarization opposite to the one polarizationto the area-wide broadcast downlink beam for broadcast transmissions. 3.A method as recited in claim 2, further comprising: assigning the fullprimary spectrum for broadcast transmissions in minimum-resolutionbroadcast bands.
 4. A method as recited in claim 3, wherein theminimum-resolution broadcast bands are assigned to any and all uplinkspot beams in any combination as configured by a network control center.5. A method as recited in claim 4, wherein each one of the multipleuplink and downlink spot beams can access the full primary spectrum forbroadcast transmissions in increments of one minimum-resolutionbroadcast band and can transmit on at least a portion of at least oneminimum-resolution broadcast band.